1. Field of the Invention
The invention disclosed herein relates to screens in vibratory or gyratory screening machines used to separate granular materials in the coal and rock aggregate industries. Specifically, it relates to an apparatus and a method for repairing holes and other damage in those screens.
2. Description of the Prior Art
In the coal mining industry, as well as the rock quarrying industry, the coal and rock aggregates produced from the mine or quarry are usually separated or classified according to the size of the aggregate fractions. In addition, mined coal usually must be “cleaned” to separate aggregates and other undesired materials from the coal.
These separation and cleaning operations are typically accomplished using gyratory or vibratory screening machines. The machines have a number of screens which are typically installed horizontally within the machine. In the machines, the coal or rock mining products are introduced onto the upper surface of the screen. The machine imparts a gyratory or vibratory motion to the screen which causes fractions of aggregate smaller than the apertures of the screen to fall through the screen, while the remaining larger fractions are discharged from the upper surface.
The screens themselves may be constructed by several designs. One design common in the coal industries comprises a plurality of parallel metal bars, with rectangular or circular cross sections. The spacing or opening between the bars is set to the desired specification of the aggregates to be classified. In another design, metal wire is woven into an open mesh with a simple weave pattern, to produce generally square openings bounded between adjacent warp and weft wires.
The rock aggregates, including those aggregate impurities contained in coal, are hard and abrasive and will cause gradual wear on the screen elements. This wear often produces holes in the screen surface. When this happens, larger fractions of the coal or rock aggregate are permitted to pass down through the screen, thereby either reducing the yield of the desired larger fraction collected from the screen or contaminating the smaller desired rock fraction passing through the screen.
When a hole is created in a screen, the screen must either be repaired or replaced. Generally, a temporary repair means is initially utilized, which can be implemented relatively quickly, until the screen can be replaced during a longer scheduled cessation of operations. Temporary methods of repair include welding steel plates to the screen or filling and sealing the hole with silicone sealant or other pliable substance. However, these methods can be either time consuming to implement or may not be sufficiently reliable.